1. Field of the Invention
The present invention relates to a semiconductor device and method for manufacturing the same.
2. Related Art
After a semiconductor wafer is produced or a semiconductor chip is fabricated, a test is conducted and, for example, a failure element is replaced with a redundant circuit and voltage values are switched to obtain a power supply voltage with a desired accuracy level, which is called trimming.
Related-art technologies employ zener zaps, which are devices required for trimming purposes. A power supply voltage is applied in advance to two input terminals of a selector circuit, and a zener zap is coupled in series between a ground terminal and each of the input terminals. One of the zener zaps with this state is selectively applied with large current, whereby heat is generated to break down the device to be short-circuited to the ground terminal. A combination of voltages input to the selector circuit is thus determined.
Such zener zaps, however, occupy some area on the wafer exclusively for trimming purposes, which inevitably increases the circuit area. This configuration also requires isolation of the zener zaps, into which large current is flown, to avoid any impact on other circuit elements. As a consequence, area efficiency remains low.
Another concern is residual resistance remaining after the breakdown of the zener zap. Further, the short-circuited state after the breakdown cannot be maintained stably, possibly resulting in an increase in resistance values or complete fracture to cause an open state.
The document mentioned below discloses a trimming technology without the use of zener zaps.
Japanese Patent Application Publication No. 8-055961 describes a technology used for a structure having a resistor provided on a surface of a semiconductor substrate, a thick insulating film provided above the resistor, a contact hole coupled to the resistor through the insulating film, a thin insulating film provided on the surface of the resistor in the contact hole, and metal wiring coupled to the contact hole. By the technology, the thin insulating film is applied with a voltage and broken down, whereby the resistor and the metal wiring are short-circuited to adjust resistance values.
The technology described in Japanese Patent Application Publication No. 8-055961, however, requires an additional step to provide an insulating film having a thickness small enough to be broken down by a lower voltage compared with the voltage required for breaking down the zener zap. This increases manufacturing steps and cost.
Furthermore, a diffusion layer serving as a resistor is also applied with the voltage for breaking down the insulating film, which may adversely affect resistance values of the diffusion layer after the breakdown of the insulating film.